The hot pressing of beryllium oxide with additives.

Abstract

The effect of variations in temperature, pressure and pressure cycle on the density vs grain size relationship was determined for hot pressed, sulphate-derived UOX beryllium oxide; the effects of selected additives on the final grain size using constant hot pressing conditions were also determined. A single-ended pressing technique, incorporating an incremental build-up in the pressing pressure, was developed to produce hot pressed specimens of near theoretical density with a uniform grain size of 25u. Smaller grain sizes were not obtained by this technique owing to the onset of discontinuous grain growth at a bulk density of 97 per cent theoretical. However, by introducing a 'dwell' or 'equilibration' time at temperature before the application of the load, a theoretically dense specimen (3.010 g/cm3) was produced with a uniform 8u grain size. Carbon was the only additive which consistently refined the grain size at all levels of addition. A hot pressed specimen of 99 per cent theoretical density and 2u grain size was obtained using a standard condition of 1500°C, 250 kg/cm2 for 25 minutes, 5 volume per cent of colloidal graphite additive.